차세대 극소형 피코 위성 HAUSAT-1(CubeSat)의 개발연구

김영현,김준태,김영석,서승원,장영근,Kim, Yeong-Hyeon,Kim, Jun-Tae,Kim, Yeong-Seok,Seo, Seung-Won,Jang, Yeong-Geun 통신위성우주산업연구회 2002 Joint Conference on Satellite Communications Vol.2002 No.-

본 논문은 한국항공대학교 우주시스템연구실에서 개발중인 극소형 피코위성 HAUSAT-1의 연구 결과 및 현황을 서술하고 있다. HAUSAT-1 은 차세대 극소형 위성으로 과기부의 지원하에 우주핵심기술의 개발을 목적으로 시행되고 있으며, 국내 대학에서 최초로 순수히 학생들에 의해 설계, 제작, 조립 및 시험과 운영되는 위성개발 프로그램이다. HAUSAT-1 은 미국의 스탠포드대학과 Cal Poly 가 주관이 되어 개발하고 있는 CubeSat 의성개발 프로젝트의 일원으로 1Kg 이하의 무게와 한 변의 길이가 10cm 를 갖는 정육면체의 형상을 갖는 극소형위성 개발프로그램이다. CubeSat 위성개발은 최소의 개발비용을 사용하여 단기간 내에 위성핵심부품의 우주인증시험을 수행하고 대학 및 대학원생들에게 위성의 전반적인 개발과정을 이해하고, 실질적인 경험을 갖도록하는 프로그램이다. HAUSAT-1 위성의 임무는 GPS 를 통한 위치정보 수집, 여분의 전력 생성을 위한 박판광태양전지의 전개시험, 다양한 차폐방법에 따른 메모리의 방사능 시험등을 수행할 예정이다. 예상되는 위성궤도의 고도와 경사각은 각각 650km 와 $65^{\circ}$이며, 2004년 초에 발사할 예정이다. This paper addresses the development and design of the HAUSAT-1 (Hankuk Aviation University SATellite-1), a new generation picosatellite, being developed by SSRL (Space System Research Lab.) of Hankuk Aviation University. This project is funded by Korean Government for the purpose of developing the space core technology. This is the first satellite development program executed at the level of university in Korea. The CubeSat project is to develop the satellite weighing less than 1 kg and provides opportunities with low construction, low launch cost space experiment platforms with shorter production cycles. The HAUSAT-1 project offers graduate and undergraduate students great opportunities to be able to understand the design process of satellite development and have practical experience as a team member. Its mission objectives are getting position data by the GPS receiver module, to deploy the thin film solar cell panel to generate extra power, and to conduct a radiation experiment on memory chips having different types of shielding material. The HAUSAT-1 will orbit at the altitude og 650 km with 65 degree inclination angle for 1 tear of design mission life. The HAUSAT-1 plans to be launched in the early of 2004.

새로운기술 받아들일려는 자세 아쉬워

김영현,Kim, Yeong-Hyeon 대한양돈협회 1990 養豚 Vol.12 No.8

중국 특허청 특허 검색 소개 및 검색 예

김영현,Kim, Yeong-Hyeon 한국특허정보원 2004 Patent 21 Vol.- No.55

사용자 선호도를 사용한 군집 기반 추천 시스템

김영현,신원용,Kim, Younghyun,Shin, Won-Yong 한국정보통신학회 2017 한국정보통신학회논문지 Vol.21 No.2

In a flood of information, most users will want to get a proper recommendation. If a recommender system fails to give appropriate contents, then quality of experience (QoE) will be drastically decreased. In this paper, we propose a recommender system based on the intra-cluster users' item preference for improving recommendation accuracy indices such as precision, recall, and F1 score. To this end, first, users are divided into several clusters based on the actual rating data and Pearson correlation coefficient (PCC). Afterwards, we give each item an advantage/disadvantage according to the preference tendency by users within the same cluster. Specifically, an item will be received an advantage/disadvantage when the item which has been averagely rated by other users within the same cluster is above/below a predefined threshold. The proposed algorithm shows a statistically significant performance improvement over the item-based collaborative filtering algorithm with no clustering in terms of recommendation accuracy indices such as precision, recall, and F1 score.

Spring rod를 사용한 척추경 나사못과 동반 시술된 Flexible cage의 생체역학적 효과

김영현,박은영,김원현,황성필,박경우,이성재,Kim, Y.H.,Park, E.Y.,Kim, W.H.,Hwang, S.P.,Park, K.W.,Lee, Sung-Jae 대한의용생체공학회 2017 의공학회지 Vol.38 No.1

Recently, flexible cages have been introduced in an attempt to absorb and reduce the abnormal load transfer along the anterior parts of the spine. They are designed to be used with the pedicle screw systems to allow some mobility at the index level while containing ROM at the adjacent level. In this study, a finite element (FE) study was performed to assess biomechanical efficacies of the flexible cage when combined with pedicle screws with flexible rods. The post-operated models were constructed by modifying the L4-5 of a previously-validated 3-D FE model of the intact lumbar spine (L2-S1): (1) Type 1, flexible cage only; (2) Type 2, pedicle screws with flexible rods; (3) Type 3, interbody fusion cage plus pedicle screws with rigid rods; (4) Type 4, interbody fusion cage plus Type 2; (5) Type 5, Type 1 plus Type 2. Flexion/extension of 10 Nm with a compressive follower load of 400N was applied. As compared to the Type 3 (62~65%) and Type 4 (59~62%), Type 5 (53~55%) was able to limit the motion at the operated level effectively, despite moderate reduction at the adjacent level. It was also able to shift the load back to the anterior portions of the spine thus relieving excessively high posterior load transfer and to reduce stress on the endplate by absorbing the load with its flexible shape design features. The likelihood of component failure of flexble cage remained less than 30% regardless of loading conditions when combined with pedicle screws with flexible rods. Our study demonstrated that flexible cages when combined with posterior dynamic system may help reduce subsidence of cage and degeneration process at the adjacent levels while effectively providing stability at the operated level.

척추경나사못을 이용한 유합술과 동반 시술된 극돌기간 삽입기구의 생체역학적 연구

김영현,박은영,이성재,Kim, Y.H.,Park, E.Y.,Lee, S.J. 대한의용생체공학회 2015 의공학회지 Vol.36 No.6

Recently, during the multi-level fusion with pedicle screws, interspinous spacer are sometimes substituted for the most superior level of the fusion in an attempt to reduce the number of fusion level and likelihood of degeneration process at the adjacent level. In this study, a finite element (FE) study was performed to assess biomechanical efficacies of the interspinous spacer combined with posterior lumbar fusion with a previously-validated 3-dimensional FE model of the intact lumbar spine (L1-S1). The post-operative models were made by modifying the intact model to simulate the implantation of interspinous spacer and pedicle screws at the L3-4 and L4-5. Four different configurations of the post-op model were considered: (1) a normal spinal model; (2) Type 1, one-level fusion using posterior pedicle screws at the L4-5; (3) Type 2, two-level (L3-5) fusion; (4) Type 3, Type 1 plus Coflex$^{TM}$ at the L3-4. hybrid protocol (intact: 10 Nm) with a compressive follower load of 400N were used to flex, extend, axially rotate and laterally bend the FE model. As compared to the intact model, Type 2 showed the greatest increase in Range of motion (ROM) at the adjacent level (L2-3), followed Type 3, and Type 1 depending on the loading type. At L3-4, ROM of Type 2 was reduced by 34~56% regardless of loading mode, as compared to decrease of 55% in Type 3 only in extension. In case of normal bone strength model (Type 3_Normal), PVMS at the process and the pedicle remained less than 20% of their yield strengths regardless of loading, except in extension (about 35%). However, for the osteoporotic model (Type 3_Osteoporotic), it reached up to 56% in extension indicating increased susceptibility to fracture. This study suggested that substitution of the superior level fusion with the interspinous spacer in multi-level fusion may be able to offer similar biomechanical outcome and stability while reducing likelihood of adjacent level degeneration.

소규모 이더넷 스위치에서 개선된 적응적 전력 제어 메커니즘

김영현,이성근,고진광,Kim, Young-Hyeon,Lee, Sung-Keun,Koh, Jin-Gwang 한국전자통신학회 2013 한국전자통신학회 논문지 Vol.8 No.3

Ethernet is the most widely deployed access network protocol around the world. IEEE 802.3az WG released the EEE standard based on LPI mode to improve the energy efficiency of Ethernet. This paper proposes improved adaptive power control mechanism that can enhance energy-efficiency based on EEE from small Ethernet switch. The feature of this mechanism is that it predicts the traffic characteristic of next cycle by measuring the amount of traffic flowing in during certain period and adjusts the optimal threshold value to relevant traffic load. Performance evaluation results indicate that the proposed mechanism improves overall performance compared to traditional mechanism, since it significantly reduces energy consumption rate, even though average packet delay increases a little bit.

구인두 폐색을 유발한 자발성 편도선 혈종 치험 1예

김영현,이종철,이형준,최정석,김보형,강성호,유명상,Kim, Young Hyun,Lee, Jong Cheol,Lee, Hyung Jun,Choi, Jung Suk,Kim, Bo Hyung,Kang, Sung Ho,Yu, Myeong Sang 대한기관식도과학회 2011 大韓氣管食道科學會誌 Vol.17 No.1

Spontaneous tonsillar bleeding is a rare condition in ENT unit. Almost reported cases have been related to infection of tonsils. Prior to introduction of antibiotics, spontaneous tonsillar bleeding was usually related to superficial capsular bleeding due to acute or chronic tonsillitis. The presented case is a 36-year old healthy man without history of acute, chronic tonsillitis, and coagulation disorder who complained of dyspnea and oropharyngeal foreign body sensation after vomitting. Examination revealed a reddish polypoid mass of the right tonsil. Furthermore, the mass pushed uvula and tongue base, caused nearly total obstruction of oropharynx. All rountine laboratory test results were within normal limits. Computed tomography (CT) showed low density mass of attached in upper pole of right tonsil without enhancement. We performed tonsillectomy including the reddish polypoid mass under general anesthesia. The pathology revealed lymphoepithelial tissue with reactive hyperplasia. This is the first reported tonsillar hematoma presenting as a large oropharyngeal mass which was caused by vomitting.

변용된 자의식 아닌 '사실적 삶의 지표'

김영현,Kim, Yeong-Hyeon 대한출판문화협회 2006 출판저널 Vol.366 No.-

영농기 필지논에서의 인 (P) 농도와 산화환원전위 (Eh)의 변화 특성

김영현,김진수,장훈,Kim, Young-Hyeon,Kim, Jin-Soo,Jang, Hoon 한국농공학회 2010 한국농공학회논문집 Vol.52 No.5

The purpose of this study is to investigate characteristics of total phosphorus (TP) and phosphate phosphorous ($PO_4$-P) concentrations in ponded water and redox potential (Eh) in paddy soil during the growing season. The TP and $PO_4$-P concentrations showed twice peak values after basal dressing and tillering fertilization. The ratio of $PO_4$-P to TP showed low values (0.07~0.18), indicating that most of phosphorus is particlulate. The $PO_4$-P concentrations significantly decreased with dissolved oxygen (DO) concentrations. The Eh showed high values (179~636 mV) under non-ponded aerobic condition, but low values (74~112 mV) under ponded anaerobic condition The TP and $PO_4$-P concentrations in ponded water increased shortly after tillering fertilization even if phosphorus was not applied. This may be due to the release of dissolved phosphorus from the bottom sediment and its associated algal and water flea blooms under anaerobic condition. Therefore, proper water management should be needed shortly after tillering fertilization.